It cites "hydrocarbon pollution, salinity and turbidity problems," adding: "No element related to sustainable development has been included in the project."

It said all of the 131 people it interviewed in affected areas had complained of state intimidation.

Nicaraguan authorities have not commented on the report.

When the scheme was unveiled in July 2014, the government said it had chosen the route so it would avoid areas of great biodiversity, indigenous territories and environmentally protected lands.

The government estimated then that the scheme would lift more than 400,000 people out of general poverty by 2018 with the help of revenues created by the project. It was given a five-year completion date.

Officials say the canal is essential to allow for increased global trade and ever larger tankers, many of which are too large for the Panama Canal, even after its current expansion.